JPH06167406A - Differential pressure type pressure change measuring device - Google Patents

Abstract

PURPOSE:To accurately measure a fine pressure change regardless of the magnitude of pressure. CONSTITUTION:A differential pressure type pressure change measuring device is equipped with a differential pressure type pressure sensor 10, the automatic back pressure adjusting mechanism 20 provided in parallel to the pressure sensor 10, the gas pipe 30 for connecting the back pressure area of the pressure sensor 10 to airtightly with the automatic back pressure adjusting mechanism 20, and the opening and closing valve 36 provided to the gas pipe 30. The differential pressure type pressure sensor 10 is airtightly partitioned into upper and lower parts by a diaphragm 12 and the gas pipe 30 is connected to the upper part. The automatic back pressure adjusting mechanism 20 is a cylindrical container 21 having an opening 22 provided to the bottom part thereof and the gas pipe 10 is connected to the upper part of the container 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring a pressure fluctuation in a liquid by supplying a gas having a constant pressure and a liquid pressure substantially equal to the surrounding liquid pressure to a back pressure side of a differential pressure type pressure sensor. Is. This device can measure minute pressure changes with high accuracy without being affected by high water pressure even when it is inserted deep into water, and is therefore useful for pressure measurement in high-depth water permeability tests and the like.

[0002]

2. Description of the Related Art In the technical field of soil investigation and the like, it has become necessary to measure minute pressure changes deep in a liquid. For example, as a typical example, there is a test for determining the water permeability of the ground by applying a water pressure to the ground and measuring the propagation velocity thereof. In this test, pressurized water whose pressure changes stepwise is injected into a boring hole excavated in the ground, and the response pressure is measured in the boring hole in the ground away from the pressing position. In addition, in the field of reservoir engineering in petroleum engineering, there is also a case where pressure is applied to a part of a reservoir of oil and its pressure propagation is measured in order to estimate the reserve of oil.

By the way, in order to measure the pressure, various differential pressure type pressure sensors are generally used. In principle, the inside is airtightly partitioned by a diaphragm, the measurement pressure is applied to one side, the back pressure (usually atmospheric pressure) is applied to the other side, and a sensor element such as a strain sensor is placed on the back pressure side. It is a configuration to be arranged. In such a pressure sensor, the deformation amount of the diaphragm due to the differential pressure between the measured pressure and the back pressure is detected by the sensor element and is taken out as a change in the electric amount such as electric resistance or voltage and converted into a pressure value. is there. Therefore, a pressure sensor is selected and used according to the measured pressure range.

[0004]

However, such a pressure sensor has a problem that it is difficult to measure minute pressure fluctuations under high pressure. As described above, in the conventional differential pressure type pressure sensor, since the measured pressure is measured from the deformation amount of the diaphragm,
Under high pressure, the diaphragm and the like must also have a strong structure that can withstand the pressure. That is, a pressure sensor for high pressure is required. However, in that case, the change in the deformation amount of the diaphragm with respect to the pressure change is reduced, and the change in the electrical output detected by the pressure sensor is also reduced. Moreover, when the change in electrical output decreases, it is buried in various noises,
It becomes difficult to retrieve the signal. That is, as the rated pressure increases, the sensitivity and resolution of the sensor decrease.

In the above-mentioned water permeability test, pressure propagation may be measured in a boring hole having a large depth of several hundreds to 1,000 m. In that case, as the measurement depth increases due to the presence of groundwater, the hydrostatic pressure applied to the pressure sensor increases. On the other hand, the pressure fluctuation to be detected becomes smaller as the distance from the pressurizing position increases in inverse proportion to the second to third power of the distance.
It is quite weak. For the above reasons, the conventional differential pressure type pressure sensor has a drawback in that it cannot satisfactorily perform a large depth water permeability test.

As a pressure sensor, a crystal vibration type has been developed in recent years. This crystal vibration type pressure sensor is a method of measuring the adhered mass as a change in the resonance frequency of the vibrator, and has a feature that absolute pressure can be measured with high sensitivity. Therefore, it can be used under high pressure and has excellent resolution. However, since it is a method of digitally measuring the resonance frequency (counting the number of vibrations within a fixed time), the measurement is performed every fixed time, and continuous measurement cannot be performed over time. In the case of the above-mentioned water permeability test, it is necessary to continuously measure the pressure propagation in time (to detect the received waveform), which is not suitable for such an application. Moreover, pressure sensors of this kind are very expensive.

An object of the present invention is to provide a differential pressure type pressure fluctuation measuring device capable of accurately measuring a minute pressure change regardless of the magnitude of the pressure.

[0008]

SUMMARY OF THE INVENTION The present invention is a differential pressure type pressure sensor which is airtightly partitioned by a diaphragm and detects the difference between the liquid pressure on the measurement side and the gas pressure on the back pressure side by the displacement thereof, and the differential pressure type pressure sensor. A back pressure automatic adjustment mechanism that is installed in parallel with the pressure sensor and generates gas at a pressure that is approximately in balance with the surrounding liquid pressure, and a gas communication that air-tightly connects the back pressure side of the differential pressure type pressure sensor and the back pressure automatic adjustment mechanism. A differential pressure type pressure fluctuation measuring device comprising a pipe and an opening / closing valve provided in the gas communication pipe.

As the automatic back pressure adjusting mechanism, there is a container having an opening at the bottom. Alternatively, it may be configured to include a container, a pipe that penetrates the wall of the container and reaches the vicinity of the bottom, and a check valve for introducing the liquid, which is provided in the pipe. The gas communication pipe is connected to the upper part of the container. A droplet trap may be provided in the middle of the gas communication pipe. In addition to this, there is also one in which a gas communication pipe is connected to the atmosphere side and a high-pressure gas generation source via a three-way valve. The automatic back pressure adjusting mechanism may be an airtight structure and an expandable / contractible bag-shaped body to which a gas communication pipe is connected. To be flexible,
The material itself may be elastic such as rubber, or may be a bellows structure.

[0010]

In the liquid, the gas inside the automatic back pressure adjusting mechanism has a pressure almost equilibrium with the liquid pressure at the surrounding depth. When the open / close valve of the gas communication pipe is opened, the gas pressure is transmitted to the back pressure side of the differential pressure type pressure sensor, while the surrounding liquid pressure is applied to the measurement side of the differential pressure type pressure sensor. Since the differential pressure type pressure sensor and the back pressure automatic adjusting mechanism are installed in parallel, the measurement pressure applied to the diaphragm and the back pressure are always substantially equal regardless of the insertion depth. Therefore, at any depth, the back pressure that is almost in equilibrium with the hydraulic pressure at that depth is automatically applied to the diaphragm automatically, and it is not necessary to make the diaphragm a strong structure. At the time of measurement, the on-off valve provided in the gas communication pipe may be closed. The on-off valve acts to isolate the influence of pressure fluctuations in the automatic back pressure adjusting mechanism. The back pressure is a constant pressure immediately before the on-off valve is closed, and the pressure fluctuation is measured based on the amount of deformation of the diaphragm at that time as a reference. The gas space prevents the inflow of liquid and prevents short-circuits and corrosion of the sensor elements and wirings installed on the back pressure side of the diaphragm.

When the back pressure automatic adjusting mechanism is a container having an opening at the bottom, liquid flows in and out through the opening, and the gas inside is balanced with the liquid pressure at the top of the container. Since the gas communication pipe is connected to the upper part of the container, by designing the capacity of the container to be sufficiently large, the liquid will not flow into the gas communication pipe.
A gas pressure that is in equilibrium with the liquid pressure will be applied to the back pressure side.

The pipe with a check valve provided in the container of the automatic back pressure adjusting mechanism allows the surrounding liquid to flow in during the process of inserting / withdrawing into / from the liquid, but even if it tilts, the internal liquid or It functions to prevent the gas from flowing out. The water drop trap prevents the liquid from reaching the pressure sensor even if the liquid has entered through the gas communication pipe due to an erroneous operation or the like. Further, the gas generating source connected to the three-way valve forcibly supplies the high-pressure gas into the container so that the upper part of the container is filled with gas even if the container volume is small.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing an embodiment of a differential pressure type pressure fluctuation measuring device according to the present invention. This differential pressure type pressure fluctuation measuring device includes a differential pressure type pressure sensor 10, a back pressure automatic adjustment mechanism 20 arranged in parallel with the differential pressure type pressure sensor 10, a back pressure side of the differential pressure type pressure sensor 10 and an automatic back pressure adjustment. Mechanism 20
And a gas communication pipe 30 that air-tightly communicates with each other, and an opening / closing valve 36 provided in the gas communication pipe 30.

The differential pressure type pressure sensor 10 has a hollow cylindrical shape, and the inside thereof is airtightly partitioned by a diaphragm 12. The upper side of the diaphragm 12 is the back pressure side, and the pressure sensor element 14 is arranged therein. A pressure introducing pipe 16 that transmits the surrounding water pressure is connected to the bottom of the differential pressure type pressure sensor 10, and a gas communication pipe 30 is connected to the upper portion. The lead wire 18 from the pressure sensor element 14 is connected to the measurement recording device 40 installed on the ground via the water resistant connector 19 on the upper side.

The automatic back pressure adjusting mechanism 20 is a metallic cylindrical container 21 having a capacity of, for example, about 800 to 1000 cc. An opening 22 through which ambient water flows in and out is provided in the bottom portion thereof, and a gas communication pipe 30 is connected to the upper portion thereof.
The gas communication pipe 30 is a thin high-pressure tube (for example, a diameter of 1 m).
m). An electromagnetic on-off valve 36 is arranged in the middle of the gas communication pipe 30, and is opened and closed by an operation from the ground.

Next, the pressure fluctuation measuring operation of this differential pressure type pressure fluctuation measuring device will be described. With the on-off valve 36 open, the differential pressure type pressure fluctuation measuring device is installed in the boring hole 42.
Insert to the prescribed depth. The surrounding water flows into the container 2 through the opening 22 provided at the bottom of the automatic back pressure adjusting mechanism 20.
The air in 1 is compressed to a pressure that is approximately in equilibrium with the hydrostatic pressure. This is applied to the back pressure side of the diaphragm 12 of the differential pressure type pressure sensor 10 via the gas communication pipe 30. On the other hand, water pressure is applied to the measurement side of the diaphragm 12 through the pressure introducing pipe 16 of the differential pressure type pressure sensor 10. here,
Since the differential pressure type pressure sensor 10 and the back pressure automatic adjusting mechanism 20 are arranged in parallel, the depth of water is substantially the same, and the back pressure and the hydrostatic pressure applied to the diaphragm 12 are substantially equal.
In this way, by the automatic back pressure adjusting mechanism 20, no matter which depth the differential pressure type pressure fluctuation measuring device is inserted, a back pressure approximately equal to the hydrostatic pressure is automatically applied to the differential pressure type pressure sensor 10. Therefore, even at high depths, the diaphragm 12
Even if the structure is for low pressure, there is no risk of destruction.
Therefore, the amount of deformation with respect to a minute pressure can be increased, and the measurement sensitivity can be increased even under high pressure. However, it should be noted here that since the back pressure is transmitted as a gas flow, there is a time lag until a predetermined back pressure is applied. Therefore, the insertion speed into the water must be so slow that the differential pressure does not exceed the rating of the differential pressure type pressure sensor 10.

After reaching a predetermined measurement depth, the gas communication pipe 3
The on-off valve 36 installed at 0 is closed. This is to prevent the automatic back pressure adjusting mechanism 20 from changing the back pressure due to the fluctuation of the surrounding water pressure. When the on-off valve 36 is closed, the back pressure automatic adjustment mechanism 20 causes the differential pressure type pressure sensor 10 to move.
The transmission of gas pressure to the is cut off, and the back pressure maintains a constant value. Using the deformation amount of the diaphragm 12 at this time as a reference, the pressure fluctuation is measured depending on how much the diaphragm 12 is deformed with respect to this reference value.

When changing the measurement depth or when pulling up the apparatus, it is only necessary to open the open / close valve 36 and restore the connection between the differential pressure type pressure sensor 10 and the automatic back pressure adjusting mechanism 20. When the device is inserted further into the boring hole 42, the hydrostatic pressure increases, water flows into the container 21 through the opening 22, and the gas pressure increases. However, the pressure on both sides of diaphragm 12 remains approximately balanced. When the device is pulled up from the boring hole 42, the hydrostatic pressure gradually decreases, and the water inside the container 21 flows out through the opening 22 and the gas pressure decreases. This action keeps the pressures on both sides of the diaphragm 12 approximately balanced during pulling. The reason why the gas communication pipe 30 has a small diameter of about 1 mm is to make the inner volume of the gas communication pipe 30 as small as possible and prevent water from entering the gas communication pipe 30 even at a large depth.

FIG. 2 is an explanatory view showing another embodiment of the differential pressure type pressure fluctuation measuring device according to the present invention. The back pressure automatic adjusting mechanism 50 of the differential pressure type pressure fluctuation measuring device includes a container 51,
A pipe 54 that penetrates the container wall to reach the vicinity of the bottom and a check valve 56 for introducing water provided in the pipe 54 are provided. The gas communication pipe 30 is connected to the upper portion of the container 51 and has a droplet trap 47 in the middle of the gas communication pipe 56. The gas communication pipe 30 is connected to the atmosphere side and the high-pressure gas generation source 46 via a three-way valve 38. High pressure gas source 46
The nitrogen gas cylinder is a precision pressure adjusting device 44. The other parts may be similar to the structure shown in FIG. 1, and therefore, the same reference numerals are given and the description thereof is omitted.

If water enters the back pressure side of the differential pressure type pressure sensor 10 through the communication pipe 30, it may damage the pressure sensor element and the like. The present embodiment can prevent such a situation from occurring more effectively. First check valve 56
Allows the inflow of water around the automatic back pressure adjusting mechanism 50, but blocks the outflow of water and air inside. Therefore, even if the back pressure automatic adjusting mechanism 50 is largely tilted in the process of inserting into water, the internal air does not flow out, and therefore the tilt can be relatively easily inserted without paying attention to the tilt.

The droplet trap 47 is a vertically long closed container 48.
And a gas inlet pipe 49 that penetrates the upper wall and reaches near the bottom surface
and a gas outlet pipe 49b that penetrates the bottom wall of the container and reaches the vicinity of the upper surface. This prevents water from entering the back pressure side of the differential pressure type pressure sensor 10 when the water flows into the gas communication pipe 30 due to an operation error or the like. That is, even if water enters the gas communication pipe 30 from the automatic back pressure adjusting mechanism 50, the infiltrated water is stored in the vertically long closed container 48 of the droplet trap 47.
Do not penetrate into the back pressure side of the differential pressure type pressure sensor 10. Therefore,
If it is desired to prevent water from entering more reliably, it is effective to provide such a droplet trap 47.

The three-way valve 38 serves to gradually release gas to the atmosphere side when pulling up the present device, and to balance the pressure on both sides of the diaphragm of the differential pressure type pressure sensor 10. The high-pressure gas generation source 46 also supplies the high-pressure gas to the back pressure automatic adjustment mechanism 50 via the three-way valve 38, thereby fulfilling the function of compensating for the shortage of the container volume. For example, when the device is lowered deep into water, the hydrostatic pressure gradually increases, the gas is compressed accordingly, and finally water tends to enter the gas communication pipe. That is the maximum usable depth of the device. If the volume of the automatic back pressure adjusting mechanism 50 is increased, the range in which the gas can be compressed expands and the gas can be inserted to a large depth, but there is a limit in terms of the relationship with the boring hole or the device configuration. As described above, if the gas pressure is increased in advance, it becomes difficult for the gas to be compressed even at a large depth, and the gas can be inserted deep into the water without increasing the volume of the back pressure automatic adjusting mechanism 50.

FIG. 3 is an explanatory view showing still another embodiment of the differential pressure type pressure fluctuation measuring device according to the present invention. The automatic back pressure adjusting mechanism 60 is a bag-shaped body made of a stretchable material such as rubber. The inside is filled with gas such as air. Back pressure automatic adjustment mechanism 60 by external water pressure
Contracts, compressing the gas inside to a pressure approximately in equilibrium with the surrounding water pressure. This is applied as a back pressure to the differential pressure type pressure sensor 10 via the gas communication pipe 30. Since the automatic back pressure adjusting device 60 does not take in any external water, it does not require a mechanism such as a droplet trap as in the above-described embodiment.

The present invention is not limited to the configuration of the above embodiment. A droplet trap, a three-way valve, a high-pressure gas generation source, or the like may be combined with the configuration of the embodiment shown in FIG. It is also possible to combine a three-way valve and a high-pressure gas generation source with the embodiment of FIG. The configuration of the pressure sensor element is arbitrary, and any element can be used as long as it can measure the differential pressure between the two sides of the diaphragm.

[0025]

According to the present invention, the automatic back pressure adjusting mechanism provided in parallel with the differential pressure type pressure sensor can automatically apply the gas having the pressure almost equal to the hydraulic pressure on the measuring side of the differential pressure type pressure sensor to the back pressure side. , It is not necessary to strengthen the diaphragm structure even at high depths. Therefore, by adopting a structure that is easily deformed, it is possible to measure pressure fluctuations with high sensitivity even under high pressure. A general inexpensive pressure sensor element for detecting the deformation of the diaphragm can be used.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a differential pressure type pressure fluctuation measuring device according to the present invention.

FIG. 2 is an explanatory view showing another embodiment of the differential pressure type pressure fluctuation measuring device according to the present invention.

FIG. 3 is an explanatory view showing still another embodiment of the differential pressure type pressure fluctuation measuring device according to the present invention.

[Explanation of symbols]

 10 differential pressure type pressure sensor 12 diaphragm 20 automatic back pressure adjusting mechanism 21 container 22 opening 30 gas communication pipe 36 on-off valve

Claims (5)

[Claims] 1. An airtight partition by a diaphragm,
A differential pressure type pressure sensor that detects the difference between the hydraulic pressure on the measurement side and the gas pressure on the back pressure side due to the displacement, and a back pressure sensor that is installed in parallel with the differential pressure type pressure sensor and that produces gas at a pressure that is approximately balanced with the surrounding hydraulic pressure A pressure automatic adjustment mechanism, a gas communication pipe that airtightly connects the back pressure side of the differential pressure type pressure sensor and the back pressure automatic adjustment mechanism,
A differential pressure type pressure fluctuation measuring device comprising an on-off valve provided in the gas communication pipe. 2. The apparatus according to claim 1, wherein the automatic back pressure adjusting mechanism is a container having an opening at a lower portion, and a gas communication pipe is connected to an upper portion thereof. 3. The automatic back pressure adjusting mechanism comprises a container, a pipe penetrating the container wall to reach the vicinity of the bottom, and a check valve for introducing liquid provided in the pipe, wherein the gas communication pipe is The apparatus according to claim 1, further comprising a droplet trap connected to an upper portion of the container and provided in the middle of the gas communication pipe. 4. The apparatus according to claim 3, wherein the gas communication pipe is connected to the atmosphere side and the high-pressure gas generation source via a three-way valve. 5. The apparatus according to claim 1, wherein the automatic back pressure adjusting mechanism is an airtight structure and is an expandable and contractible bag-like body, to which a gas communication pipe is connected.